Alport-type glomerulopathy: evidence for diminished capillary loop size

Hereditary nephropathy of the Alport type is morphologically characterized by a specific and diagnostic thinning and splitting lesion of the glomerular basement membranes, which can be recognized only by electron microscopy. The light microscopical aspect has not been considered to be characteristic until now. This paper describes a light microscopical constellation of glomerular alterations by which ATGP can be recognized with high probability. Three histological features are of importance: 1. ATGP glomeruli in patients older than 10 years of age mostly have smaller capillary loops than age-matched controls. However, during the first 10 years of life no difference in glomerular capillary loop size was noticed. 2. ATGP loops often stain less intensely with basement membrane stains. 3. Presence of fetal-like glomeruli. Using this triad of light microscopic parameters as a screening tool, ATGP-cases were found without knowledge of any clinical data among other glomerulopathies with a sensitivity of 72% and a specificity of 93%. The definitive diagnosis, however, depends on electron microscopy.